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/home/lodo1995/src/gcc_build/gcc/include/stddef.h:1:25: fatal error: stddef.h: No such file or directory
But I can open that file with "more" without problems.
I'm on Ubuntu Server 15.10. I configured and compiled binutils without problems. I also configured gcc and compiled it with "make all-gcc". I'm using "x86_64-w64-mingw32" as target.
Mingw is usually a hosted environment. When you compile libgcc, you are using the new compiler you have created to compile a library for the target. As such, it expects all of the target's header files to be available (specifically, GCC's stddef.h includes the mingw system stddef.h). I'm guessing you don't have the mingw headers anywhere (or at least anywhere your compiler can find them). You may want to look at the mingw.org site to see their compilation instructions.